In a hybrid car or an electric car which have become popular in recent years, downsizing and weight reduction of a motor which is a power source are strongly required. As one means of downsizing, there is a concept of enhancing a pacing factor of conductors in a slot of a stator coil of a rotating machine, to enhance a power density. To realize this, instead of a conventional structure in which continuous magnet wire or enameled wire is assembled into a slot, a so-called segment-coil-winding technique is used. In the segment-coil-winding technique, a coil conductor is divided into a large number of segment coils which are bent into a predetermined shape and assembled into a slot and then the segment conductors are electrically connected to each other.
Meanwhile, the hybrid car and the electric car are based on the premise that they are motor-driven by an inverter. As driving voltage of the motor-driving inverter is increased, in the stator coil of the segment-coil-winding technique, insulating paper (slot liner) is inserted in between segment coil/stator core and between different phase coils in the segment winding in the slot to secure electrical insulation of the stator core and between coil phases (see PTL 1).